Coiled tube fluid heater



Jan. 23, 1968 J. P. NORTON 3,364,902

COILED TUBE FLUID HEATER Filed. May 4, 1966 2 Sheets-Sheet l Fig. 3

J i V ENTOR.

John P A/ovzon Jan. 23, 1968 J. P. NORTON 3,364,902

COILED TUBE FLUID HEATER Filed May 4, 1966 2 Sheets-Sheet 2 INVENTOR. t/a/m ,Q A/orzon /M fi United States Patent Ollice 3,364,532 Patented Jan. 23, 1968 3,364,902 COILED TUBE FLUID HEATER John P. Norton, St. Louis, Mo., assignor to American Air Filter Company, Inc., Louisville, Ky., a corporation of Delaware Filed May 4, 1966, Ser. No. 547,658 Claims. (Cl. 122-249) ABSTRACT OF THE DISCLOSURE An apparatus for heating a heat sensitive fluid which includes a coiled tube to carry the fluid to be heated, a combustion shroud to receive hot gases from a combustion source disposed in spaced relation from the coil to form an annular area therebetween, sealing means to prevent flow of gas through the annular area between the coil and the combustion shroud, and means to direct the products of combustion emitted from the shroud to heat contact relation with the surface of the coil opposite the surface exposed to the shroud.

In some previous coiled tube fluid heaters, which have included a flame generating heat source, direct impingement of combustion products and flame on the fluid carrying tube has resulted in localized overheating of the tubes so such heaters have been unsatisfactory for heating thermal sensitive fluids. While such an arrangement promotes heat transfer, impingement of flames on the tubes also promotes pitting and corrosion of the tubes and deposition of carbon on the tubes which causes localized hot spots leading to reduced life of the fluid heater.

In other previous coiled tube fluid heaters, a combustion shroud has been interposed between the flame from the heat source and the coiled tubes to direct the flames and prevent direct impingement of the flame on the coiled tubes. In some such previous fluid heaters, having a shroud interposed between the flame and the coiled tube, there has been conductive heat transfer between the shroud and the tubes while in other fluid heaters combustion products have been permitted to pass between the shroud and the tubes. Where there has been conductive heat transfer between the shroud and the coil, localized overheating has occurred in the contact areas so the tube and the fluid are heated to extremely high temperatures and these heaters have been unsatisfactory for heating thermal sensitive fluids at acceptable thermal efliciencies.

In accordance with the present invention, a novel coiled tube fluid heater is provided which is useful to heat thermal sensitive fluids at significantly improved thermal efliciencies without overheating the coil in localized areas. Furthermore, the coiled tube fluid heater in accordance with the present invention, which includes a combustion shroud to direct flames emitted from the heat source, provides improved efliciency of radiant heat transfer from the combustion shroud to the fluid coil, advantageously promotes transfer of heat from the combustion products to the coil by conductive or convective heat transfer without direct impingement of the flame on the coils, and provides a heater arrangement having an improved overall heat transfer efliciency. The straightforward heater in accordance with the present invention can be made of economical lightweight materials and the flow resistance encountered by combustion products passing through the shell side of the heater is very low so an inexpensive, low 'pressure, heat source can be used.

Various other features of the present invention will become obvious to one skilled in the art upon reading the disclosure set forth hereinafter.

More particularly, the heater of the present invention provides: an outer casing including a first end and a second end; gas exhaust means from the casing; heat source means having an outlet disposed to direct heat through said first end into the casing; a combustion shroud extending into the casing having an inlet end disposed to receive heat from the heat source and an outlet end to direct such heat into the casing; a fluid carrying tube having an fluid inlet and a fluid outlet, said tube being wound into a coil having a minimum diameter greater than the greatest diameter of the shroud, said coil being disposed in surrounding relation to the shroud in spaced relation therefrom to form an annular opening between the shroud and the coil; and, coil sealing means extending across the annular area from the outer surface of the shroud to the coil to restrict passage of gas in an axial direction through the annular space formed between the shroud and the coil.

It is to be realized that various changes can be made in the construction or arrangement of the fluid heater disclosed herein without departing from the scope or intent of the present invention.

Referring now to the drawings:

FIG. 1 is a plan view, partly in section, of a fluid vaporizer in accordance with the present invention;

FIG. 2 is a plan view, partly in section, of a combustion shroud and coiled fluid carrying tube for a fluid heater in accordance with the present invention; and,

FIG. 3 is a view taken in a plane passing through line 3-3 of FIG. 1.

FIG. 1 shows, generally, a fluid heater in accordance with the present invention which can advantageously be used to vaporize a heat sensitive fluid. The fluid heater of FIGURE 1 has an outer casing 16 adapted to receive an internal heater assembly comprising a coiled tube 3 surrounding a tubular combustion shroud 2 with the coil and the shroud joined to annular flange 4 which is fastened to casing 16 along the outer periphery thereof. The axis of coil 3, which coil surrounds shroud 2, substantially coincides with the axis of shroud 2 and the heater assembly including coil 3 and shroud 2 is disposed in casing 16 at an angular relation to the longitudinal axis of casing 16 as hereinafter described. The fluid heater of the example of FIG. 1 also includes heat source 1, which can be a fuel burning flame generating burner, joined to annular flange 4 in communicative relation with shroud 2 through the aperture of such flange.

In accordance with the present invention, the smallest or inner diameter of coil 3 is greater than the maximum or outer diameter of shroud 2 so an annular area 14 (FIG. 2) is provided between coil 3 and the periphery of shroud 2. The annular separation between coil 3 and shroud 2 prevents conductive heat transfer from shroud 2 to coil 3 but advantageously permits radiant heat transfer through the area.

Ordinarily, the temperature of shroud 2 is extremely high, especially when heat source 1 is of the flame generating type, and if conductive heat transfer were permitted between shroud 2 and coil 3 the temperature of coil 3 would approach the temperature of shroud 2, a temperature at which most fluids except water decompose or deteriorate. Therefore, in accordance with the present invention, there is no direct contact between shroud 2 and coil 3 so the temperature of coil 3 does not approach the undesirably high temperature of shroud 2 but radiant heat transfer is promoted between shroud 2 and coil 3. Since the rate of radiant heat transfer for a given temperature differential is low, relative to the rate of conductive heat transfer, coil 3 is not heated to an undesirably high temperature in spite of the extremely high temperature differential between shroud 2 and coil 3. Furthermore,

Q heat transferred to coil 3 from shroud 2 by radiation is absorbed by the fluid carried in the coil, and so long as the fluid flow rate through the coil compares favorably with the rate of heat transferred to coil 3 by radiation there is no accumulating heat build-up in the coil.

In the example ofFIG. 1 an inside annular flange 4 is joined to the inlet end of casing 16. An outside annular flange 18 surrounds the inlet end of shroud 2 and heat source 1 terminates in an outlet end including an annular flange 5. Annular flanges 5 and 18 are joined to flange 4 so the outlet of heat source 1 and the inlet of shroud 2 are in aligned communicative relation through the aperture in flange 4. Shroud 2 extends toward end 22 of casing 16 and terminates in an outlet 11 through which combustion products from heat source 1 are emitted into casing 16. Advantageously, shroud 2 is disposed in casing 16 at an oblique angular relation between end plate 22 and the iongitudinal axis of casing 16 so combustion products emitted from outlet 11 are deflected toward the side of casing 16 opposite the side in which gas emission outlet 19 is located. In the example of FIG. 1 the face of the inlet of shroud 2 is slanted so shroud 2 is disposed in casing 16 at an angle relative to the longitudinal axis of casing 16 and combustion products emitted from outlet 11 thenimpinge upon plate 2 and are deflected toward the side of casing 16 opposite outlet 19.

If shroud 2 were to be disposed in casing 16 so the longitudinal axis of the shroud and the casing are parallel and end plate 22 were disposed generally transverse the longitudnal axis of casing 16, combustion products emitted from the outlet would impinge directly on plate 22. It has been recognized that combustion products impinging directly on plate 22 would ordinarily seek the shortest path to outlet 19 so gas flow would predominantly flow through area 24 (FIG. 1) with less gas flow through area 24A. By disposing shroud 2 at a selected angle so outlet 11 is directed toward end plate 22 at an oblique angle, combustion products are deflected off end plate 22 at an angle and more of the combustion products pass through area 24A so, advantageously, there i better distribution of the combustion products in casing 16. By equalizing and distributing gas flow through casing 16 more contact, and better heat transfer, is obtained between the combustion products and coil 3 so the thermal efliciency is improved.

In another example of means to improve gas flow in casing 16, end plate 22 can include gas directing means (not shown) to direct combustion products emitted from outlet 11 in a smooth pattern in a selected direction within casing 16 or additional gas exhaust means can be provided in spaced relation around casing 16.

Combustion products emitted from outlet 11 pass through annular areas 24 and 24A to give up a portion of the heat remaining from the combustion process. Advantageously, the heat is given up to coil 3 by conductive or convective heat transfer to further heat the fluid in coil 3 and improve the overall thermal efliciency of the heater.

Further in accordance with the persent invention, it has been recognized that heater efliciency can be increased by improving radiant heat transfer from shroud 2 to coil 3 and in the example of FIG. 1 radiant heat transfer is improved by detering gas flow through the annular area between shroud 2 and coil 3 where radiant heat transfer is desired. T l the example of the figures, if gas flow were not restricted through annular area 14 the gas flowing through annular area 14 would be exposed to radiation from shroud 2 and absorb a portion of the radiant heat which would otherwise be transferred to coil 3. The heat so absorbed by the gases would be lost from the heater when the combustion products were omitted through outlet 19 and the loss would significantly reduce the efliciency of the heater.

In accordance with the present invention suitable means are provided to restrict the flow of combustion gases through annular area 14 between shroud 2 and coil 3 through which heat is transferred by radiation emitted from shroud 2. In the example of FIG. 1, a peripheral flange 10 is joined, for example by welding, around outlet 11 of shroud 2 to hold a cooperative sealing block 9 between a first end of coil 3 and flange 10 to prevent gas flow into and through annular area 14. Sealing block 9 is, advantageously, adapted to provide one bearing surface resting on flange 1t and an upper bearing surface resting against the first end of coil 3 to effectively close the area between coil 3 and flange it to gas flow. To further restrict the flow of gas and preventcombustion gases entering annular area 14- by passing between a second end of coil 3 and flange 4, a second sealing block 9A is provided adjacent the second end of coil 3 and adapted to have one sealing surface resting on flange 4 and a second sealing surface urged against coil 3 to provide a gas impervious sealing member between flange 4 and coil 3. Sealing blocks 9 and 9A can be cooperatively adapted to compress coil 3 between the upper and lower sealing blocks when the heater arrangement is assembled so adjacent turns of the coil are urged to contiguous relation to restrict passage of gas between adjacent turns into annular area 14. Furthermore, compressing coil 3 so adjacent turns are held in contiguous relation advantageously improves the efliciency of radiant heat transfer by preventing the undesirable escape of radiant heat between adjacent turns of the coil so the radiant heat is lost to combustion products passing through area 24 and 24A. Radiant heat which escapes from the annular area to heat combustion products in annular area 24 is lost from the heater when combustion products are exhausted from casing 16 and'the loss significantly reduces the thermal efiiciency of the heater.

It will be realized that where thermal efliciency'is not a significant factor, as where the combustion gases pass from the heater to other equipment, without secondary contact between the coil and the combustion products, the apparatus in accordance with the present invention can be used to transfer only radiant heat emitted from shroud 2, When combustion products emitted from outlet ll are not immediately exhausted from casing 16, but are reof the coil can be coated with a permanent dark substance I to improve ability'of the coil to absorb radiation emitted from shroud 2.

In the example of the figures, the outer surface of shroud 2 is corrugated The corrugations increase the total area of the shroud i.e., the emitting surface, and since radiant heat transfer is also a function of the area of the emitting and receiving surfaces, the increased area resulting from the corrugation advantageously increases the rate of radiant heat transfer to shroud 2 from coils 3.

The example of the fluid heater in accordance with the present invention as shown in the figures provides a heater having relatively few flow obstructing components so there is little resistance to gas flow through the casing. Therefore, a relatively low cost, inexpensive heat source which can operate at a low combustion pressure can be used to provide heat and expensive high pressure air supply means are not required for the heat source.

The heater of the present invention, as shown in the figures, can be made of separate components which, ad-

vantageously, can be adapted to be easily and rapidly assembled or disassambled. In the example of FIG. 2, the heater element as shown in FIG. 1 is preassembled and held together by bolts 6. As bolts 6 are drawn up tight, sealing blocks 9 and 9A compress coils 3 a selected amount to provide the proper spacing between adjacent turns of the coil or to compress coil 3 so the adjacent coils are in contiguous relation. The assembled heating element is then inserted in casing 16 and flange 4 is joined to flange 17 by means of bolts 17A.

The arrangement hereinbefore described is adequate to hold shroud 2 and coil 3 in casing 16 but additional support can be provided for the casing if desired. In the example of FIG. 1, triangular shaped wedges 27 are provided to rigidly support coil 3 in a desired position. Wedges 27 inserted through the end of casing 16 (as shown in FIG. 3) have two ends bearing on the wall of casing 16 with one end bearing on a selected turn of coil 3. When, as in the example of the figures, 3 wedges are used they can advantageously be placed at approximately 120 relative to each other to provide a stable configuration to hold coils 3 firmly in casing 16. In the example of FIG. 1, the wedges are inserted through the end of casing 16 and end plate 22 can then be fastened to flange 23 of casing 16 by bolts 26.

In an alternative embodiment (not shown) support members can be fastened to the casing 16 and extend to shroud 2 at a point adjacent outlet 11 so shroud .2 is fastened to flange 4 at the inlet end and is supported by the support members at the outlet end.

To improve thermal efliciency of the heater and promote the transfer of heat to coil 3, casing 16 and end plate 22 can be insulated to prevent undesirable loss of heat to the atmosphere.

The invention claimed is:

1. A coiled tube fluid heater comprising: an outer casing including a first and a second end; gas exhaust means for said casing; heat source means having an outlet d sposed to direct hot gas through said first end into said casing; tubular combustion shroud means extending 1nto said casing having an inlet end disposed to receive hot gas from said heat source and an outlet end to direct such hot gas into said casing; fluid carrying tube means having a fluid inlet and a fluid outlet, said tube being in the form of a coil and disposed in spaced relation from said shroud so the longitudinal axis of said shroud and said coil are substantially coincident to define an annular area between said shroud and said coil; coil sealing means extending across said annular area from the outer surface of said shroud to said coil to deter flow of gas in an axial direction through said annular area between said shroud and said coil; and means to direct hot gas emitted from said outlet of said shroud means over the surface of said coil opposite the surface exposed to said shroud.

2. The heater of claim 1 including end means closing said second end of said casing where said gas exhaust means is positioned adjacent said first end of said casing.

3. The heater of claim 2 including means to direct gases emitted from said combustion shroud against said end means at an oblique angle.

4. The heater of claim 1 including: annular flange means adjacent said inlet end of said casing with said heat source outlet means joined to said annular flange means in communicative relation with the aperture in said flange, and said inlet of such combustion shroud means joined to said inlet flange means in communicative relation with said aperture to receive hot gas and combustion products from said heat source.

5. The apparatus of claim 4 including first sealing ring means extending from said inlet flange to said fluid carrying coil to deter the flow of gases between said flange and said coil to said annular area.

6. The apparatus of claim 5 including: a peripheral flange adjacent said outlet of said combustion shroud, extending outwardly from said shroud; second seal ring means extending from said peripheral flange means to said fluid carrying coil means wherein said first and second seal ring means are of selected configuration and size to compress said coil to urge adjacent turns of said coil to contiguous relation.

7. The heater of claim 1 including: a peripheral flange adjacent the outlet of said combustion shroud, extending from said combustion shroud outwardly and second seal ring means extending from said flange means to said fluid carrying coil means.

8. The heater of claim 1 including: means to direct gases emitted from said outlet of said shroud in a direction away from said gas exhaust means.

9. The apparatus of claim 1 including: means to dispose said shroud means in said casing so the longitudinal axis of said shroud means is at an angle relative to the longitudinal axis of said casing so said shroud is slanted toward a side of said casing opposite the side having said gas exhaust means.

10. A coiled tube fluid heater comprising: an outer casing including an inlet end, an outlet end, a gas exhaust adjacent said inlet end, and, an annular flange means disposed adjacent said inlet end; heat source means joined to said flange in communicative relation with the aperture in said flange to direct heat into said casing; tubular combustion shroud means having an inlet disposed to receive heat from said heat source, said shroud extending into said casing and having outlet means to direct heat into said casing, means to dispose said combustion shroud in said casing at an angular relation relative to the longitudinal axis of said casing so said outlet means is directed toward said second end of said casing where said shroud slants toward a side of said casing generally away from said gas exhaust; fluid carrying tube means having a fluid inlet and a fluid outlet, said tube being wound into a coil having a diameter greater than the diameter of said shroud and said coil being disposed to surround said shroud so the axis of said shroud and said coil are substantially coincident and said coil is disposed in spaced relation from said shroud to form an annular opening between said shroud and said coil; first sealing ring means extending from said inlet flange to said fluid carrying coil to deter flow of gas into said annular area between said inlet flange and said coil; a peripheral flange adjacent said outlet of said combustion shroud, said flange means extending outwardly from said combustion shroud; and, second seal ring means extending from said flange means to said fluid carrying coil means to deter flow of gas into said annular area between said shroud and said coil wherein said first and second seal ring means are disposed to compress said coil so adjacent turns of said coil are held in contiguous relation.

References Cited UNITED STATES PATENTS 1,609,661 12/1926 Quinn et al 122250 2,645,210 7/ 1953 Harris et al 122-248 3,065,741 11/1962 Gerard 122250 3,246,634 4/1966 Stevens 122-356 CHARLES J. MYHRE, Primary Examiner, 

